Multi-layer tablet with recess, device and method for compacting such a tablet

ABSTRACT

The invention relates to a press device for manufacturing compacted tablets from at least one mixture in powder form, comprising at least one compaction assembly comprising a lower punch ( 3 ) and an upper punch ( 4 ) each having an active compaction surface and placed on either side of a die, in which the lower punch has a longitudinal recess open on the side of the die, inside of which is mounted a central rod which is translatably mobile relative to the lower punch, characterised in that the central rod is coupled to the lower punch by means of a resilient link provided so as to hold, in an inoperative position, the central rod in a maximum deployed position in which the central rod protrudes relative to the active surface of the lower punch. The invention also relates to a specific compaction method and to a multi-layer compacted tablet with a recess.

FIELD OF THE INVENTION

The present invention relates to multilayer tablets having a cavity, andto a rotary press to form such a tablet and associated productionmethod. The proposed invention can be useful for example in the field ofthe production of disinfectant tablets e.g. to purify water, ordetergent tablets intended to be used in appliances of dishwasher orwashing machine type for the cleaning of eating utensil or laundryelements respectively.

STATE OF THE ART

Detergent tablets are most often prepared by mixing various componentstogether, preferably in powder or granule form, but also in liquid form.This mixture is then compacted using a press to form a tablet.Nonetheless in detergent tablets some components ill withstandcompression, others may react before use and thereby reduce the efficacyof the tablet at the time of use, this being the reason why multilayertablets have been developed such as described in patent applicationEP0979862. Multilayer tablets allow separation of ingredients likely toreact and at the same time allow compression-sensitive ingredients to becompressed only once by inserting them in the last layer for example.Multilayer tablets may have slightly deferred disintegration timesbetween the different layers, the first layer having been compressedseveral times generally having a longer disintegration time than thefollowing less compressed layers.

Other formats of tablets have also been developed such as so-called “tabon tab” tablets formed of a conventional monolayer or multilayer tableton which a portion of tablet is positioned e.g. in the form of asemi-sphere. The “tab on tab” format allows separation of incompatiblecompounds in the different layers whilst improving the appearance of thetablets. With this tablet format, it is also possible to obtainsequenced disintegration of the different tablet phases. Such tabletsand associated production methods are described for example in thedocuments WO01/98448, WO01/49815, EP1179042 and EP1244767.

Application WO2006/048606 describes a method of producing a multilayertablet having a cavity intended to receive an insert such as a bead, thecavity being formed using a compaction method by stamping. Morespecifically, in a rotary press with punches for example, compaction bystamping provides for an upper punch comprising an active compactingsurface having a profile with a projecting portion for the purpose offorming the cavity in the different compacted layers. With such acompacting method, the areas below and in the vicinity of the sides ofthe cavity are compressed to a much larger extent than the remainder ofthe tablet which creates density heterogeneities within the tablet. Suchdensity heterogeneities result in the different areas of one layerhaving different disintegration and solubilisation profiles, this alsoacting on the mechanical strength of the tablets.

To overcome these disadvantages, it was proposed in applicationWO00/10800 to use a press device in which the lower and upper puncheseach comprise a ring-shaped part and a central part able to moveindependently of one another. Such a press device allows the forming ofmultilayer tablets in which one of the layers is ring-shaped, whilst thelayer immediately adjacent to this ring-shaped layer covers the latterand even fully fills the central cavity of the ring-shaped layer. Such atablet has the advantages of having relatively homogeneous mechanicalproperties, in particular in terms of density, and is visually close toan insert tablet of “tab on tab” type, this being of some commercialinterest. However, the proposed production method is complex toimplement since it particularly requires independent controlling of thedifferent parts forming the lower and upper punches. In addition, thetablets formed using such a method have a certain number ofdisadvantages in terms of disintegration in particular. ApplicationEP1440790 also describes a press device of this type, allowing theproduction of tablets of most diverse shapes, but the layout andfunctioning of the device are very complex.

Another method was described in application WO01/85437 and proposessimplifying the previously described method using a conventional upperpunch and a lower punch comprising a ring-shaped portion able to bemoved in translation, and a central coaxial element inside thering-shaped portion of the lower punch, the central element being heldduring the entire compaction cycle, in particular during actualcompression, in a determined fixed position where said central elementis in the die underneath the upper surface of the die. The describedmethod allows the forming of tablets having a cavity without the centralrod being moved during the different steps of the compacting cycle. Thetablets produced with such a method may comprise several layers, one ofthe end layers comprising a blind cavity inside which an insert of “tabon tab” type may be inserted for example. The tablets thus formed havethe advantage of relatively homogeneous mechanical properties inparticular in terms of density, and allow true tablets of “tab on tab”type to be produced. However, the functional properties of said tabletsstill remain to be improved, in particular in terms of disintegration.

It is therefore one goal of the invention to propose a compactedmultilayer tablet with cavity which does not have the above-mentionedshortcomings.

In particular, it is one goal of the invention to propose a compactedmultilayer tablet with cavity which has increased functional properties,in particular in terms of disintegration.

It is also a goal of the invention to propose a compacted multilayertablet with cavity which has improved mechanical properties, havinghomogeneous density distribution for example, and having mechanicalstrength allowing good tablet handling and storage.

Another goal of the invention is to propose a rotary press with improvedpunches, allowing the forming of compacted multilayer tablets withcavity in simple manner and on an industrial scale.

A further goal of the invention is to propose a rotary punch presshaving specific functional elements that can easily be adapted to aconventional rotary punch press.

A further goal of the present invention is to propose a method ofproducing a compacted multilayer tablet with cavity that is easy toproduce, in particular not requiring any specific control or commanddiffering from a method of producing a compacted multilayer tablet nothaving a cavity.

DESCRIPTION OF THE INVENTION

For this purpose, a press device is proposed to produce compactedtablets from at least one mixture in powder form, comprising:

-   -   a rotary table in which is arranged at least one die intended to        receive the mixture,    -   at least one compaction assembly comprising a lower punch and an        upper punch each having an active surface for compaction, said        lower and upper punches being arranged on either side of the        table with their respective active surface facing the die, and        being mounted movable in translation coaxially to the die and        following the rotating movement of the table,    -   wherein the lower punch comprises a longitudinal cavity open on        the side of the die, inside which a central rod is mounted        movable in translation with respect to the lower punch along an        axis of translation,        characterized in that the central rod is coupled to the lower        punch via a resilient link provided along the translation axis        of the central rod to hold, in the rest position, the central        rod in a deployed position in which the central rod projects        with respect to the active surface of the lower punch.

This deployed position preferably corresponds to the maximum deployedposition i.e. the abutting position of the central rod with respect toits translational movement outwardly from the lower punch.

Preferred but non-limiting aspects of this device, taken alone or incombination, are the following:

-   -   the upper punch has a planar or curved solid active surface,    -   the central rod is integral with the lower punch so that, if no        stress is applied to the central rod, said central rod remains        in a fixed position with respect to the lower punch when said        lower punch is moved,    -   the resilient link has a spring constant provided so that the        central rod moves towards inside the longitudinal cavity of the        lower punch subsequent to stress applied by the upper punch when        said upper punch is moved close to the lower punch,    -   the resilient link has a sufficient spring constant so that the        central rod remains at least partly projecting from the active        surface of the lower punch when the upper punch is moved close        to the lower punch,    -   the resilient link has a spring constant of between 0.1 daN/mm        and 10 daN/mm, preferably between 0.2 daN/mm and 4 daN/mm, more        preferably between 0.5 daN/mm and 3 daN/mm, and further        preferably between 1 daN/mm and 2.5 daN/mm.    -   the device comprises a resilient link member inserted between        the central rod and the lower punch to form the resilient link,        the resilient link member preferably being selected from among a        spring, a resilient compression rod or a pneumatic cylinder,    -   the device comprises an actuating member fixedly mounted on the        central rod and extending radially with respect to said central        rod, said actuating member projecting laterally from the lower        punch through a groove arranged in said lower punch, said        actuating member being provided to abut against the die so as to        position the central rod in a retracted position in which the        central rod does not project from the active surface of the        lower punch.

There is also proposed a method of producing a compacted multilayertablet with cavity using such a press device.

In particular, a method is proposed of producing a compacted tablethaving at least two layers using a press device such as presented,comprising the following successive steps:

-   -   E1. Taking a first mixture in powder form and placing said first        mixture in an open space formed by the lower punch and the die,        so as to cover the active surface of said lower punch and the        central rod projecting from said active surface;    -   E2. Moving the upper punch close to the lower punch so as to        apply a compaction stress on the first mixture to form a first        compacted layer, said compaction stress further allowing        movement of the central rod towards inside the longitudinal        cavity;    -   E3. Moving the upper punch away from the lower punch so as to        remove the compaction stress on the first mixture so that the        central rod returns to its deployed position with respect to the        lower punch, the central rod thereby piercing the first layer so        as to form a through cavity;    -   E4. Taking a second mixture in powder form and placing said        second mixture in the open space formed by the lower punch and        the die, so as to cover the first layer;    -   E5. Moving the upper punch close to the lower punch so as to        apply a compaction stress on the second mixture and the first        layer to form a second compacted layer on the first layer;    -   E6. Moving the upper punch away from the lower punch so as to        remove the compaction stress on the compacted assembly formed by        the first and second layers;    -   E7. Ejecting the compacted assembly out of the die by        translation of the lower punch so that the active surface of        said lower punch lies flush with the surface of the rotary        table, the compacted assembly thus ejected forming the compacted        tablet.

Preferred but non-limiting aspects of this method, taken alone or incombination, are the following:

-   -   at the ejection step E7, the movement of the lower punch in the        direction of the die allows movement of the central rod to a        retracted position in which the central rod does not project        from the active surface of the lower punch;    -   before the ejection step E7, the successive steps E4, E5 and E6        are reiterated as many times as it is desired to add additional        layers to the compacted assembly;    -   before the ejection step E7, an additional compacting step is        performed by moving the upper punch close to the lower punch so        as to apply an additional compaction stress to the compacted        assembly.

Finally, a compacted multilayer tablet is proposed wherein each layer isformed from a mixture in powder form, comprising:

-   -   a first layer with a through cavity along a longitudinal axis        orthogonal to the first layer; and    -   at least one second layer directly formed on the first layer;        characterized in that the second layer fills less than 70% of        the volume of the cavity of the first layer.

By construction, the first layer is the only pierced layer of thetablet.

Preferred but non-limiting aspects of this tablet, taken alone or incombination, are the following:

-   -   the second layer has a surface flush with the surface of the        first layer without the second layer extending into the cavity        of the first layer;    -   in the tablet, the percentage compaction of the mixture of        compacted powder at the cavity differs from the percentage        compaction of the whole multilayer tablet by less than 5%,        preferably less than 3%, and more preferably less than 1%.    -   the different layers are formed from powder mixtures for        detergent or disinfectant action.

DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will becomefurther apparent from the following description that is solelyillustrative and non-limiting and is to be read in connection with theappended drawings in which:

FIG. 1 is a three-dimensional, cross-sectional illustration of a rotarypress device;

FIG. 2 is a schematic illustrating the driving in rotation of thepunches in the rotary press device;

FIGS. 3a and 3b are cross-sectional views of the lower punch of theinvention, in deployed position and in retracted position respectively;

FIGS. 4a and 4b are detailed cross-sectional views of the lower punch inFIGS. 3a and 3b , in deployed position and retracted positionrespectively;

FIGS. 5a and 5b are perspective views of the lower punch in FIGS. 4a and4b , in deployed position and retracted position respectively;

The series of FIG. 6, from FIGS. 6a to 6l , illustrate the differentsteps of the compacting cycle to form a compacted multilayer tablet withcavity according to the invention;

FIG. 7a is a perspective view of a compacted multilayer tablet withcavity according to the invention;

FIG. 7b is a perspective, cross-sectional view of the tablet illustratedin FIG. 7 a.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective cross-section of a rotary press device allowingillustration of the structure conventionally used to drive thecompacting punches in rotating movement.

The rotary press device comprises a turret that is set in rotation by aknown motorisation system via a drive shaft that is generally central.The turret comprises a central table 1 which comprises at least onecompacting die 2, this die 2 being intended to receive a mixture ofcompounds in powder form from which it is desired to form a compactedtablet of determined volume.

The central table preferably comprises a plurality of dies 2, forexample distributed around the periphery of the central table 1 which isof substantially circular shape. Said dies 2 are of general cylindricalshape and are either formed by a through hole directly arranged on theperiphery of the central table 1, or each die is a specific partcomprising a central cylindrical through opening of circular section andof determined diameter corresponding to the desired diameter of thetablet, this part acting as die having an external shape adapted to beinserted in the through openings arranged on the periphery of thecentral table 1.

The press device further comprises compaction assemblies each formed ofa pair of punches (not illustrated in FIG. 1), namely a lower punch andan upper punch that are arranged either side each of the dies 2 of thecentral table 1. Preferably, the device comprises a pair of lower 3 andupper 4 punches for each of the dies 2 of the device. The lower 3 andupper 4 punches are mounted in the press so that they can be movedaxially with respect to the corresponding die 2, so that said lower 3and upper 4 punches can be inserted in the die 2 to compress the powdermixture placed inside the die to form a tablet of determined volume.

The lower 3 and upper 4 punches are also mounted in the press so as tohave a circular movement corresponding to the circular movement of thedie 2 with which they are associated. One solution to set the punches inmovement along this circular trajectory is to use driving plates 5 and 6located either side of the central table 1, these two driving plates 5and 6 being integral with the central table 1 and therefore also beingmounted in rotation in the press. The driving plates 5 and 6 areprovided with through openings disposed on their periphery, thesethrough openings being intended to receive the lower 3 and upper 4punches respectively. The lower 3 and upper 4 punches are thereforedriven in rotation by the driving plates 5 and 6 respectively, insynchronised fashion with the corresponding die 2, the lower 3 and upper4 punches also being able to slide in the openings provided on theperiphery of the driving plates 5 and 6 so that the active compactingsurfaces 32 and 42 at the compacting end of the lower 3 and upper 4punches respectively are able to be inserted in the die 2.

The axial movement of the lower 3 and upper 4 punches is controlled bylower control means and upper control means respectively, these lowerand upper control means being intended to cooperate with the guidingends 31 and 41 of the lower 3 and upper 4 punches respectively. Thepurpose of the control means is to move the corresponding punches alongthe axis of the die so as to modify the axial position of the punch (andmore particularly the axial position of the compacting end of the punch)as a function of the press operating cycle. The axial position of apunch is defined as the position of the punch in the axis of the die,this position thereby allowing characterization of the axial movement ofthe punch but also the associated confinement volume.

The lower and upper control means comprise all known elements allowingthe movement of the upper and lower punches, such as cam tracks and/orcompacting rollers. These different elements are selected and assembledaccording to the specifically required compacting cycle to form thedesired tablet.

As illustrated in FIGS. 3a, 3b, 4a, 4b, 5a and 5b , the proposed pressdevice has the particularity of comprising a lower punch 3 with a mainbody 33 comprising a longitudinal cavity 34 open on the side of the die2 on the side of the active surface 32. A central rod 35 is mountedinside this longitudinal cavity 34 so that it is movable in translationwith respect to the lower punch 3. The sliding central rod 35 is alsocalled a sliding finger.

As illustrated in FIGS. 3a and 3b , the main body 33 of the lower punch3 is generally mounted on a punch holder forming the guiding end 31 ofsaid lower punch 3.

The central rod 35 is advantageously coupled to the lower punch 3 via aresilient link 36 provided along the axis of translation of the centralrod 35 in the longitudinal cavity 34.

The resilient link 36 is provided to hold in the rest position thecentral rod 35 in deployed position in which the central rod 35 projectsfrom the active surface 32 of the lower punch 3. As illustrated in FIGS.3a, 4a, and 5a , this deployed position is the maximum deployed positioni.e. the central rod 35 is unable to slide further outwardly from thebody of the lower punch 3. The arrangement of the central rod 35 isprovided for example such that this central rod abuts an internal wallof the body 33 of the lower punch 3 thereby limiting its outwardtranslation and hence defining the maximum deployed position.

The central rod 35 is preferably integral with the lower punch 3 so thatwhen no stress is applied to the central rod 35, said central rod 35remains in a fixed position with respect to the lower punch 3 when saidlower punch 3 is moved.

Therefore, unless a specific stress is applied to the central rod 35,the movements of said central rod 35 remain highly dependent onmovements of the body 33 of the lower punch 3.

Preferably, the central rod has passive movement i.e. it is the movementof other parts of the press device which drive the movement of thecentral rod 35, in particular movement of the lower punch 3 and/or upperpunch 4.

The proposed specific arrangement allows the central rod 35 to be movedand optionally to have its position modified with respect to the body 33of the lower punch 3, without any direct actuating of said central rod35. It is chiefly the movement of the upper punch 4 with respect to thelower punch 4 which allows movement of the central rod 35 with respectto the body 33 of the lower punch 3. It is to be noted that the upperpunch 4 may be of conventional shape, in particular with a simple activesurface i.e. without cavity or projection, but on the contrary having asolid surface. Therefore, the upper punch 4 has a planar active surfaceor a curved surface if it is desired that the outer surface of thetablet should be curved, but in all cases the surface is solid.

The movement of the central rod 35 with respect to the body 33 of thepunch 3 is dependent on the resilient link 36 between these parts.

The resilient link 36 may be formed for example of a resilient linkmember 36 inserted between the central rod 35 and the lower punch 3.

Such a resilient link member 36 may be a spring for example asillustrated in the different Figures. This spring is preferably acompressive spring extending from one end of the central rod 35 in thelongitudinal cavity 34 and bearing upon an inner wall of the body 33 ofthe lower punch 3.

However, the resilient link member could be any other element ensuringthe required function for the resilient link. For example, the use couldbe envisaged of a resilient compression rod. A pneumatic cylinder couldalso be used.

According to one preferred embodiment, the resilient link is ensuredthrough the use of Belleville washers. Belleville washers are discs witha specific shape that ensure a spring function.

Preferably, the resilient link 36 has a spring constant provided so thatthe central rod 35 moves inwardly into the longitudinal cavity 34 of thelower punch 3 subsequent to stress applied by the upper punch 4 whensaid upper punch 4 is moved close to the lower punch 3.

As will be seen below, one of the objectives is to produce a multilayertablet having a cavity, and more specifically a multilayer tablet inwhich one of the end layers has a through cavity so that it is possibleto access the immediately adjacent layer via this through cavity.

When the upper punch 4 is moved close to the lower punch 3, thecompacted powder mixture forms a compacted layer having a blind cavity,this cavity corresponding to the volume of the central rod 35 projectingfrom the active surface 32 of the lower punch 3. The fact that thecentral rod 35 partly retracts when a certain compaction stress isapplied means that this same central rod 35 will be deployed on releaseof the compaction stress so that it comes to pierce the film closing theblind cavity to create a through cavity.

More preferably, the resilient link 36 has a sufficient spring constantfor the central rod 35 to remain at least partly projecting from theactive surface 32 of the lower punch 3 when the upper punch 4 is movedclose to the lower punch 3.

The fact that the central rod 35 is able to remain at least partlyprotruding from the active surface 32 of the lower punch 3 guaranteesthat the cavity formed in the first compacted layer is never fullyfilled. In particular, when the powder mixture intended to form theadjacent layer is compacted, this mixture can partly fill the cavity ofthe first layer, in particular if a high compaction stress is applied.

Further preferably, the resilient link has a spring constant of between0.1 daN/mm and 10 daN/mm, preferably between 0.2 daN/mm and 4 daN/mm,more preferably between 0.5 daN/mm and 3 daN/mm, and further preferablybetween 1 daN/mm and 2.5 daN/mm.

The selected spring constant may be a function of the applied compactionforce. Therefore, preferably, a resilient link is chosen adapted for acompaction force of between 10 kN and 500 kN, preferably between 20 kNand 200 kN, and more preferably between 30 kN and 150 kN.

As indicated above, and as will be seen more precisely from thedescription of the compaction method below, the central rod 35 has axialmovement inside the longitudinal cavity 34 which is dependent upon thecompaction stress applied to the powder mixture to be compacted, thiscompaction stress being dependent upon the relative position of thelower 3 and upper 4 punches.

In some phases of the compacting cycle, and in particular when theformed compacted tablet is ejected, it is preferable that the centralrod 35 should be in retracted position in which it does not project fromthe active surface 32 of the lower punch 3 i.e. the central rod 35 isfully inside the longitudinal cavity 34.

This makes it possible for the compacted tablet to be removed veryeasily from the rotary table 1 of the press e.g. via sweeping to pushthe tablet radially out of the rotary table 1.

For this purpose, the lower punch 3 preferably comprises an actuatingmember 37 fixedly mounted on the central rod 35 and extending radiallyfrom said central rod 35.

This actuating member 37 projects laterally from the body 33 of thelower punch 3 through a groove 38 arranged inside the lower punch 3.

The actuating member 37 may be ring-shaped for example, surrounding thebody 33 of the lower punch 3.

This actuating member 37 is provided to come and abut the die 2 when thelower punch 3 is moved in the direction of said die 2. Once theactuating member 37 is in abutment, the movement of the lower punch 3 inthe direction of the die 2 tends to cause the central rod 35 to enterthe longitudinal cavity 34 until it is positioned in the retractedposition in which the central rod 35 no longer projects from the activesurface 32 of the lower punch 3.

One of the advantages of the device presented above is that it isadaptable to any standard rotary press i.e. any press havingconventional upper and lower punches with a solid body and activesurface mounted at the end of the body.

It suffices to replace the lower punch of a standard rotary press withthe lower punch presented above, to form a press device allowing theproduction of tablets having complex shapes, in particular multilayeredand with cavity as described below. Most advantageously, the presentedlower punch is able in particular to cooperate with any type of upperpunch, it simply being necessary to adapt the stiffness of the resilientlink on which depends the movement of the central rod.

FIGS. 6a to 6l illustrate a method of producing a compacted multilayertablet with cavity using a press device such as presented above.

At step E1, a first mixture in powder form is first taken that isintended to compose the first layer 110 of the tablet 100 provided witha cavity 111.

The upper punch 4 is brought to raised position. The lower punch 3 isbrought to bottom position with the central rod 35 in maximum deployedposition under the action of the resilient link 36.

As illustrated in FIG. 6 a, the first mixture is then placed in the openspace formed by the lower punch 3 and the die 2 so as to cover theactive surface 32 of said lower punch 3 and the central rod 35projecting from said active surface 32. For example, the powder fillsthe entirety of the cavity formed by the die 2 and the lower punch 3.

FIG. 6b illustrates the dosage of the first mixture to maintain theexact amount required for compaction of the first layer. The upper punch4 is still in top position and the lower punch 3 rises into the die 2 soas to maintain only the desired amount of first powder mixture.

Preferably, the height of powder to be compacted substantiallycorresponds to the height of the projecting portion of the central rod 5protruding from the active surface 32 of the punch 3. More preferably, athin layer of powder of between 0.05 mm and 1 mm covers the central roditself.

At the following step E2, such as illustrated in FIG. 6 c, the firstpowder mixture is compacted. For this purpose, the upper punch 4 ismoved close to the lower punch 3 so as to apply a compaction stress onthe first mixture to form a first compacted layer, said compactionstress further allowing movement of the central rod 35 towards theinside of the longitudinal cavity 34. The compacted layer thus formedhas a blind cavity such as described above, this blind cavitycorresponding to the volume of the central rod 35 remaining projectingfrom the active surface 32 of the lower punch 3.

At the following step E3, such as illustrated in FIG. 6d , the upperpunch 4 is moved away from the lower punch 3 to remove the compactionstress on the first mixture and so that the central rod 35 returns toits deployed position with respect to the lower punch 3 under the actionof the resilient link 36. The central rod 35 therefore pierces the firstlayer thereby forming a through cavity in the place of the blind cavityformed at the preceding step.

Next, the second compacted layer is formed on this first pierced layer.A second mixture in powder form is therefore taken at step E4, intendedto compose the second layer 120 of the tablet 100.

As illustrated in FIG. 6e , the second mixture is placed in the openspace formed by the lower punch 3 and the die 2, so as to cover thefirst compacted layer.

FIG. 6f illustrates the dosage of the second mixture to maintain theexact amount desired for compaction of the second layer. The upper punch4 is still in raised position and the lower punch 3 moves up into thedie 2 so as only to hold the desired amount of second powder mixture.

At the following step E5, such as illustrated in FIG. 6f , the secondpowder mixture is compacted on the first compacted layer. For thispurpose, the upper punch 4 is moved towards the lower punch 3 to apply acompaction stress on the second mixture and the first layer to form asecond compacted layer on the first layer.

Under the compaction stress, and as a function of the spring constant ofthe resilient link 36, the central rod 35 can be moved towards insidethe longitudinal cavity 34. If the central rod 35 moves beyond thecontact surface between the first compacted layer and the second powdermixture, then the second compacted powder mixture will partly fill thethrough cavity 111 of the first compacted layer 110.

At the following step E6, the upper punch 4 is moved away from the lowerpunch 3 to remove the compaction stress on the compacted assembly formedby the first and second layers.

If it is desired to form a tablet with cavity having only two layers, itis possible at step E7 to eject the compacted assembly from the die 2via translation of the lower punch 3. Before this ejection, anadditional compaction stress is applied to the two-layer compactedassembly thus formed to reinforce the cohesion of the assembly andthereby finalize compaction of the compacted product.

If it is desired to form a tablet with cavity having more than twolayers, the successive steps E4, E5 and E6 are repeated as many times asthere are desired additional layers on the compacted assembly.

Therefore, as illustrated in FIGS. 6h to 6k , a third layer 130 can beformed on the two-layer compacted assembly. To do so a third mixture inpowder form is collected that is intended to form the third layer 130 ofthe tablet 100.

As illustrated in FIG. 6h , the third mixture is placed in the openspace formed by the lower punch 3 and the die 2 to cover the secondcompacted layer.

FIG. 6i illustrates the dosage of the third mixture so as to maintainthe exact amount desired for compaction of the third layer. The upperpunch 4 is still in raised position and the lower punch 3 moves up intothe die 2 so as only to hold the desired amount of third powder mixture.

At the following step illustrated in FIG. 6 j, the third powder mixtureis compacted on the two-layer compacted assembly. To do so the upperpunch 4 is moved towards the lower punch 3 to apply a compaction stresson the third mixture and the two-layer compacted assembly to form athird compacted layer on the two-layer compacted assembly.

To finalize compaction, an additional compaction stress is applied tothe three-layer compacted assembly to reinforce the cohesion of theassembly. Therefore, as illustrated in FIG. 6 k, in addition to downwardmovement of the upper punch 4 the lower punch 3 can also be movedupwards increasing the compaction stress.

The upper punch 4 is then moved away from the lower punch 3 to removethe compaction stress on the three-layer compacted assembly, and torelease the die 2.

At previously described step E7, illustrated now in FIG. 6 l, thethree-layer compacted assembly is ejected out of the die 2 bytranslation of the lower punch 3. The lower punch 3 is raised so thatthe active surface 32 of said lower punch 3 comes to lie flush with thesurface of the rotary table. The ejected compacted assembly forms thedesired compacted tablet.

Preferably, the movement of the lower punch 3 in the direction of thedie 2 at the ejection step E7, allows movement of the central rod 35 toa retracted position in which the central rod 35 does not project fromthe active surface of the lower punch 3. This facilitates the ejectionstep of the formed, compacted tablet. It is achieved for example bymeans of an adapted actuating member 37 integral with the central rod35, as described above in detail.

The above-described specific rotary press and method allow theproduction of multilayer tablets wherein the different layers have aparticular arrangement allowing advantageous mechanical but alsofunctional properties to be imparted to the compacted tablet.

In this manner compacted multilayer tablets are produced wherein eachlayer is formed from a mixture in powder form, comprising a first layerhaving a specific form with a through cavity along its longitudinal axisand at least one second layer formed directly on the first layer andhaving a form similar in dimension to the first layer.

The first layer can also be called the pierced layer of the tablet. Aswill be seen below, this first layer is the only layer having a throughorifice formed by means of the specific arrangement of the central rodin the lower punch.

One specificity of the formed tablet is that the second layer fills lessthan 70% of the volume of the cavity of the first layer. Since thesecond layer is not pierced, the cavity of the first layer is uniformlyand progressively filled starting from the contact surface between thefirst and second layer. The volume of the cavity of the first layer thatis not filled with the constituent material of the second layer istherefore located on the side of the free surface of the first layer.

Preferably, the second layer fills less than 50% of the volume of thecavity of the first layer, preferably less than 30% of the volume of thecavity of the first layer, further preferably less than 20% of thevolume of the cavity of the first layer and even less than 10% of thevolume of the cavity of the first layer.

According to another preferred embodiment, the second layer has asurface flush with the surface of the first layer without the secondlayer extending into the cavity of the first layer. The second layertherefore does not at all enter the inside of the through cavity of thefirst layer.

FIGS. 7a and 7b a particular embodiment of a compacted three-layertablet 100 such as produced for example with the above-described method,comprising a first layer 110 pierced with a through cavity 111,associated with a second layer 120 and a third layer 130 on the secondlayer 120.

According to this embodiment, the second layer 120 lies flush with thethrough cavity 111 without the powder of the second mixture enteringinto the through cavity 111.

The fact that the through cavity 111 of the first layer 110 is mostlyfree of composition forming the second layer 120 results in theimparting of specific properties to the tablet that are particularlyadvantageous and will become more clearly apparent from the testsdescribed below.

In particular, such an arrangement can guarantee good disintegration ofthe different layers. The disintegration of the second layer 120 ispromoted in particular by the fact that the contact with the solution ismade not only on the peripheral edges but also inside the through cavity111. In addition, since the second layer 120 has little or no extensioninside this through cavity 110, the disintegration of the first layer110 is not perturbed.

In all configurations, as follows from the production method describedabove, and as follows also from the Figures, the second layer and theoptional other additional layers do not have a through cavity. They arenon-pierced layers contrary to the first layer.

The fact that only the first layer is pierced and that the other layeror layers are non-pierced allows a tablet to be produced havingsufficient strength for handling and storage of the tablet, whilst beingof complex design with the possibility in particular of seeing thesecond layer through the through cavity of the first layer which ispierced.

The general shape of the compacted multilayer tablet, and hence of thedifferent constituent layers thereof, can be diverse according to needsof use e.g. of octagonal, rectangular, oval, circular or othercross-section. Preferably, the compacted tablet is of circularcross-section and hence of general cylindrical shape.

Similarly, the cavity 111 formed through the first layer 110 may have adiverse cross-section e.g. circular, square, rectangular,diamond-shaped, star-shaped or other. The shape of the through cavity111 is defined by the shape of the central rod 35, in particular thecross-section thereof.

The dimensions of the tablet and of the cavity of the pierced layer areselected as a function of the desired action and functioning of thetablet. In particular, for a detergent tablet, the shape and dimensionsof the layers and cavity are chosen as a function of the desireddisintegration sequences and times.

Preferably, the through cavity is defined by a cavity height (hc) totablet height (ht) ratio of between 5% and 80%, and more preferably ofbetween 10% and 50%.

Preferably, the through cavity is defined by a ratio of cavity surface(Sc) to tablet surface (St) of between 2% and 70%, and more preferablyof between 5% and 40%.

For example, for a multilayer tablet of substantially cylindrical shape,with a cavity of circular cross-section, the diameter of the cavity isbetween 5% and 80% of the diameter of the first tablet layer, andpreferably between 10% and 60%.

Aside from the advantages presented above in connection with thespecific arrangement of the layers with respect to one another, theproposed compacted multilayer tablet has the particularity of relativelyhomogeneous percentage compaction throughout the tablet, in particularwhether at the cavity or in the tablet as a whole. In addition, thepercentage compaction at the through cavity is low in comparison withthe cavities obtained with prior art technologies, in particular viastamping or fixed rod. This makes it possible to further improve thedisintegration times of the tablets, in particular by eliminating theformation of hard cores.

Preferably, the percentage compaction of the compacted powder at thethrough cavity is close to the percentage compaction of the wholemultilayer tablet. Preferably, the percentage compaction of thecompacted powder at the cavity differs from the percentage compaction ofthe whole multilayer tablet by less than 5%, more preferably by lessthan 3%, and further preferably by less than 1%.

Comparative tests were performed as set out below to highlight theadvantages imparted to the compacted multilayer tablets by the proposedcompaction method using the specifically developed rotary press.

More specifically, the tests allowed a comparison to be made between thetablets formed using different technologies, in particular with amovable upper punch and fixed protruding rod (stamping technique), witha fixed lower punch having a fixed protruding rod, or using the proposedmethod with a fixed lower punch having a projecting rod mounted on aspring.

Experimental Conditions

The objective is to measure the percentage compaction of the compactedpowder contained in the cavity of the tablets and the disintegrationtime of the tablets. The tablets were therefore obtained using thefollowing technologies:

-   -   fixed upper punch with rod (stamping method);    -   fixed lower punch with fixed rod;    -   fixed lower punch with spring-mounted rod (method of the        invention)

Handlings are performed on a hydraulic press.

The true density of the powder used was measured on a helium pycnometerof Ultrapycnometer 1000 type by Quantachrome using the followingprotocol:

-   -   the product to be analyzed is weighed in a cell;    -   the cell is then placed in the measuring chamber of the        pycnometer;    -   the measuring chamber is closed and measurement initiated;    -   on completion of measurement, the true density of the analyzed        product is obtained.

The principle of this measurement is to inject a gas such as helium at agiven pressure into a reference chamber, then to expand this gas in themeasuring chamber containing the sample and measure the new pressure ofthe gas in this chamber. This method is particularly adapted formeasurement of volumes and densities of divided or porous solids sincethe gas enters the cavities.

The percentage compaction (T) is defined by the following formula:

T=(da/dv)*100

where:

-   -   da is the apparent density of the compacted solid product,    -   dv is the true density of the powder before compaction.

Apparent density (da) is determined using the following formula:

da=m/V=m/(S*h)

where:

-   -   m is the mass of the compacted solid product, in grams    -   V is the volume of the compacted solid product in cm3,    -   S is the surface area of the compacted solid product in cm2,    -   h is the height of the compacted solid product in cm, measured        using a vernier caliper after ejection of the solid product from        the die of the press used for compaction.

The formed tablets have a cylindrical shape with a diameter of 32 mm.The cavity is also of cylindrical shape with a diameter of 10 mm.

For the stamping method, the following elements were used:

-   -   a fixed cylindrical lower punch of diameter 32 mm, with planar        circular active surface;    -   a die with cylindrical cavity of diameter 32 mm;    -   a movable cylindrical upper punch of diameter 32 mm, with planar        circular active surface having a fixed projecting rod, the rod        having a diameter of 10 mm and projecting from the active        surface of the punch by 3.84 mm.

For the method using a fixed lower punch with fixed rod, the followingelements were used:

-   -   a fixed cylindrical lower punch of diameter 32 mm, with a planar        circular active surface having a fixed projecting rod, the rod        having a diameter of 10 mm and projecting from the active        surface of the punch by 3.84 mm;    -   a die with cylindrical cavity of diameter 32 mm;    -   a movable cylindrical upper punch of diameter 32 mm, with a        planar circular active surface.

For the method of the invention using a fixed lower punch with a springmounted rod, the following elements were used:

-   -   a fixed cylindrical lower punch of diameter 32 mm, with a planar        circular active surface having a movable projecting rod mounted        on a spring (spring constant of 1.05 daN/mm and length of 20        mm), the rod having a diameter of 10 mm and projecting beyond        the active surface of the punch in deployed position by 5.62 mm;    -   a die having a cylindrical cavity of diameter 32 mm;    -   a movable cylindrical upper punch of diameter 32 mm, with a        planar circular active surface.

A bilayer tablet was produced in which the composition of the powdermixtures for the two layers was identical. One of two layers weighed13.5 g and the other of the two layers weighed 4.5 g, i.e. a tabletweighing a total of 18 g. The tests were successively performed for adishwasher formula, washing machine formula and disinfectant formula.

A pre-compaction force of 5 kN (i.e. a pressure of 6.2 MPa) was appliedto the first layer and final compaction of 40 kN (i.e. a pressure of49.7 MPa) was applied for the dishwasher formula and for thedisinfectant formula to compress the two layers of the tablet. A finalcompaction of 30 kN (i.e. a pressure of 37.3 MPa) was applied for thelaundry formula.

Tests Performed on a Dishwasher Detergent Powder

The dishwasher detergent powder used was composed of the ingredientsdetailed in following Table 1:

TABLE 1 Amount Ingredient (wt. %) Dense sodium carbonate 34.3Polycarboxylate 3.65 Sodium silicate 10.06 Non-ionic surfactant 2.94Sodium chloride 9 Trisodium citrate dihydrate 24.08 Sodium sulfate 7.94Cellulose 1.8 PEG 1500 5.62 Magnesium stearate 0.05 Glycerine 0.56 TOTAL100.00

The true density of this detergent powder measured as describedpreviously on the helium pycnometer was 2.0171 g/cm3.

The measurements of percentage compaction of the compacted powdercontained in the cavity of the tablets, and the disintegration times ofthe tablets obtained with the three previously described technologiesare given in Table 2 below.

The disintegration time of the tablets obtained was measured on raisingand lowering equipment with a frequency of 60 strokes/min. The tabletswere placed in a basket having multiple holes for passing of water. Thebaskets were immersed in beakers containing 1.8L of water at 30° C. Thedisintegration time was recorded once the tablet had completelydisintegrated and there were no tablet residues left in the basket.

TABLE 2 Percentage compaction of the compacted Percentage powder at thecompaction Tablet tablet cavity of the tablet disintegration Technologyused (%) (%) (min) Fixed upper punch with 95 76 8.5 fixed rod (stamping)Fixed lower punch with 84 77 10.5 fixed rod Lower punch with 78 77 7spring-mounted rod (invention)

Tests Performed on a Laundry Detergent Powder

The laundry detergent powder used was composed of the ingredientsdetailed in following Table 3:

TABLE 3 Amount Ingredient (wt. %) Sodium silicate + sodium carbonatemixture 16.5 Soap 80:20 Palm/Coconut 0.76 Non-ionic surfactant + zeolite3.995 Modified zeolite 3.995 Anionic surfactant 8.96 Microcrystallinecellulose 1.45 Sodium percarbonate 36.86 Sodium silicate 1.96 Trisodiumcitrate dihydrate 22.49 Optical brightener 1.69 Optical brightener 0.11Sodium hedphosphonate 1.12 Magnesium stearate 0.11 TOTAL 100.00

The true density of this detergent powder measured as describedpreviously was 1.7508 g/cm3.

Measurements of percentage compaction of the compacted powder containedin the cavity of the tablets, and the disintegration times of thetablets obtained with the three previously described technologies aregiven in Table 4 below.

The disintegration time of the tablets obtained was measured staticallyin a 1L beaker of water at 20° C. The disintegration time was recordedonce the tablet had fully disintegrated.

TABLEAU 4 Percentage compaction of the compacted Percentage powder atthe compaction Tablet tablet cavity of the tablet disintegrationTechnology used (%) (%) (min) Fixed upper punch with 91 79 >10 fixed rod(stamping) Fixed lower punch with 86 79 >10 fixed rod Lower punch with83 79 1.1 spring-mounted rod (invention)

Tests Performed on a Disinfectant Formula

The disinfectant powder used was composed of the ingredients detailed infollowing Table 5:

TABLE 5 Amount Ingredient (wt. %) Sodium dichloroisocyanurate dihydrate80.77 Sodium bicarbonate 11.54 Adipic acid 7.69 TOTAL 100.00

The true density of this disinfectant powder measured as describedpreviously was 1.8641 g/cm3.

Measurements of percentage compaction of the compacted powder containedin the cavity of the tablets, and the disintegration times of thetablets obtained with the three previously described technologies aregiven in Table 6 below.

The disintegration time of the tablets obtained was measured staticallyin a 1L beaker of water at 20° C. The disintegration time was recordedonce the tablet had fully disintegrated.

TABLE 6 Percentage compaction of the compacted Percentage powder at thecompaction Tablet cavity of the of the tablet disintegration Technologyused tablets (%) (%) (min) Fixed upper punch with 93 78 8 fixed rod(stamping) Fixed lower punch with 85 81 8.75 fixed rod Lower punch with76 78 5 spring-mounted rod (invention)

All the tests presented above show that the multilayer tablets formedwith the proposed method have very homogeneous percentage compactionwithin the tablet, in particular between the percentage compaction ofthe compacted powder at the cavity and the percentage compaction of thewhole multilayer tablet.

On the contrary, it is ascertained that the tablets formed with theprior art methods have percentage compactions which vary substantiallywith respect to tablet area.

Also, the described tests show that the proposed tablets have improveddisintegration properties since the disintegration time is stronglyreduced.

Additionally, the above conclusions are valid irrespective of thecomposition forming the tablet, this being most advantageous.

BIBLIOGRAPHIC REFERENCES

-   -   EP0979862    -   WO01/98448    -   WO01/49815    -   EP1179042    -   EP1244767    -   WO2006/048606    -   WO00/10800    -   WO01/85437    -   EP1440790

1. A press device to produce compacted tablets from at least one mixturein powder form, comprising: a rotary table in which is arranged at leastone die intended to receive the mixture, at least one compactionassembly comprising a lower punch and an upper punch each having anactive surface for compaction, said lower and upper punches beingarranged on either side of the table with their respective activesurface facing the die, and being mounted movable in translationcoaxially to the die and following the rotating movement of the table,wherein the lower punch comprises a longitudinal cavity open on the sideof the die, inside which a central rod is mounted movable in translationwith respect to the lower punch along an axis of translation,characterized in that the central rod is coupled to the lower punch viaa resilient link provided along the translation axis of the central rodto hold, in a rest position, the central rod in a maximum deployedposition in which the central rod projects with respect to the activesurface of the lower punch, the resilient link having a spring constantprovided so that the central rod moves towards inside the longitudinalcavity of the lower punch subsequent to stress applied by the upperpunch when said upper punch is drawn close to the lower punch.
 2. Thedevice of claim 1, wherein the central rod is integral with the lowerpunch so that, if no stress is applied to the central rod, said centralrod remains in a fixed position with respect to the lower punch whensaid lower punch is moved.
 3. The device of claim 1, wherein the upperpunch has a planar or curved solid active surface.
 4. The device ofclaim 1, wherein the resilient link has a sufficient spring constant sothat the central rod remains at least partly projecting from the activesurface of the lower punch when the upper punch is drawn close to thelower punch.
 5. The device of claim 1, wherein the resilient link has aspring constant of between 0.1 daN/mm and 10 daN/mm.
 6. The device ofclaim 1, comprising a resilient link member inserted between the centralrod and the lower punch to form the resilient link.
 7. The device ofclaim 1 comprising an actuating member fixedly mounted on the centralrod and extending radially with respect to said central rod, saidactuating member projecting laterally from the lower punch through agroove arranged in said lower punch, said actuating member beingprovided to abut against the die so as to position the central rod in aretracted position in which the central rod does not project from theactive surface of the lower punch.
 8. A method of producing a compactedtablet having at least two layers using a rotary press device,comprising the following successive steps: E1. Taking a first mixture inpowder form and placing said first mixture in an open space formed by alower punch and a die arranged in a rotary table, so as to cover anactive surface of said lower punch and a central rod projecting fromsaid active surface, said central rod being mounted within alongitudinal cavity of the lower punch movable in translation withrespect to said lower punch; E2. Moving an upper punch close to thelower punch so as to apply a compaction stress on the first mixture toform a first compacted layer, said compaction stress further allowingmovement of the central rod towards inside the longitudinal cavity; E3.Moving the upper punch away from the lower punch so as to remove thecompaction stress on the first mixture so that the central rod returnsto its deployed position with respect to the lower punch, the centralrod thereby piercing the first layer so as to form a through cavity; E4.Taking a second mixture in powder form and placing said second mixturein the open space formed by the lower punch and the die, so as to coverthe first layer; E5. Moving the upper punch close to the lower punch soas to apply a compaction stress on the second mixture and the firstlayer to form a second compacted layer on the first layer; E6. Movingthe upper punch away from the lower punch so as to remove the compactionstress on the compacted assembly formed by the first and second layers;E7. Ejecting the compacted assembly out of the die by translation of thelower punch so that the active surface of said lower punch lies flushwith the surface of the rotary table, the compacted assembly thusejected forming the compacted tablet.
 9. The method of claim 8 wherein,at the ejection step E7, the movement of the lower punch in thedirection of the die allows movement of the central rod to a retractedposition in which the central rod does not project from the activesurface of the lower punch.
 10. The method of claim 8, wherein beforethe ejection step E7, the successive steps E4, E5 and E6 are reiteratedas many times as it is desired to add additional layers to the compactedassembly.
 11. The method of claim 8 wherein, before the ejection stepE7, an additional compacting step is performed by moving the upper punchclose to the lower punch so as to apply an additional compaction stressto the compacted assembly.
 12. A compacted multilayer tablet, whereineach layer is formed from a mixture in powder form, comprising: a firstlayer with a through cavity along a longitudinal axis orthogonal to thefirst layer so as to form a pierced layer; and at least one second layerdirectly formed on the first layer; characterized in that the firstlayer is the only pierced layer of the tablet and the second layer fillsless than 70% of the volume of the cavity of the first layer.
 13. Thetablet of claim 12, wherein the second layer has a surface flush withthe surface of the first layer without the second layer extending intothe cavity of the first layer.
 14. The tablet of claim 12, in which thepercentage compaction of the mixture of compacted powder at the cavitydiffers from the percentage compaction of the whole multilayer tablet byless than 5%.
 15. The tablet of claim 12, in which the percentagecompaction of the mixture of compacted powder at the cavity differs fromthe percentage compaction of the whole multilayer tablet by less than3%.
 16. The tablet of claim 12, in which the percentage compaction ofthe mixture of compacted powder at the cavity differs from thepercentage compaction of the whole multilayer tablet by less than 1%.17. The tablet of claim 12, wherein the different layers are formed frompowder mixtures for detergent or disinfectant action.
 18. The device ofclaim 1, wherein the resilient link has a spring constant of between 0.2daN/mm and 4 daN/mmm.
 19. The device of claim 1, wherein the resilientlink has a spring constant of between 0.5 daN/mm and 3 daN/mm.
 20. Thedevice of claim 1, wherein the resilient link has a spring constant ofbetween 1 daN/mm and 2.5 daN/mm.
 21. The device of claim 1, comprising aresilient link member inserted between the central rod and the lowerpunch to form the resilient link, said resilient link member beingchosen among a spring, a resilient compression rod or a pneumaticcylinder.